Room temperature reddish-yellow electroluminescence in manganese-doped silicon light-emitting diodes

Silicon (Si) is an indirect band-gap semiconductor that does not efficiently emit light. Here, by utilizing optical transitions between the $p$-$d$ hybridized orbitals of manganese (Mn) atoms doped in Si, we demonstrate Si-based light-emitting diodes (LEDs) that continuously emit reddish-yellow visible light at room temperature. The Mn $p$-$d$ hybrid states are excited by hot holes that are accelerated in the depletion layers of reverse biased Si p-n junctions. Above a threshold reverse bias voltage of about -4 V, our LEDs show strong visible light emission with two peaks at $E_{\mathrm{1}}=$ 1.75 eV and $E_{\mathrm{2}}=$ 2.30 eV, corresponding to optical transitions from the $t_{\mathrm{-}}^{\mathrm{a}}$ (spin-down anti-bonding) states to the $e_{\mathrm{-}}$ (spin-down non-bonding) states, and from the $e_{\mathrm{-}}$ to the $t_{\mathrm{+}}^{\mathrm{a}}$ (spin-up anti-bonding) states as predicted by ab initio calculations. The internal quantum efficiency of the $E_{\mathrm{1}}$ and $E_{\mathrm{2}}$ transitions is 3 - 4 orders of magnitude higher than that of the indirect band-gap transition. We also demonstrate direct amplitude modulation of our LEDs at 1 Mbps. Our results open a way to utilize the 3d orbitals of transition metals in Si-based photonic devices.